Matt O'Riley has completed his season-long loan move from Brighton to Marseille, the club announced on Tuesday.
O'Riley, 24, will link up with former Brighton manager Roberto de Zerbi at Marseille.
"Matt has the opportunity to challenge himself at the highest level in France and in the Champions League," Brighton head coach Fabian Hürzeler said.
"We have a lot of competition in the midfield positions, and while we see Matt's long-term future here with us, this gives him the potential of more game time.
"We will monitor his progress throughout the season with Marseille, and we wish him well for the rest of the season."
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Sunderland made the move after Chelsea looked to recall Marc Guiu from his loan at the club following Liam Delap's injury at the weekend.
O'Riley, who has four caps for Denmark, signed for Brighton from Celtic in August 2024. After his £25 million ($33.5m) transfer, he made 25 appearances for Brighton and scored three goals.
João Pedro, Simon Adingra, Julio Enciso, Pervis Estupiñán, ValentÃn Barco, Tariq Lamptey and Abdallah Sima all left Brighton on permanent deals over the summer while Evan Ferguson, Facundo Buonanotte, Igor Julio and Jeremy Sarmiento left on loan.
